The present invention relates to an automatic focusing camera.
There have been well known in the art the cameras such as those produced and marketed by Polaroid Co. Ltd. which are provided with an ultrasonic distance measuring instrument which produces the signal representative of a distance to a subject by measuring a time interval from the time when a pulse of ultrasonic sound is transmitted to the subject to the time when the pulse reflected from the subject is received. These cameras comprise a camera body and a photographic lens integral therewith, so that it is impossible to change the photographic lenses. As a result, the radiation or directivity pattern of the ultrasonic beam transmitted from the ultrasonic distance measuring instrument is uniquely determined depending upon the angle of view of the photographic lens used.
However, in the case of a camera which is provided with an ultrasonic distance measuring instrument and which permits the use of various interchangeable photographic lenses, if the directivity is uniquely determined depending upon the angle of view of a standard photographic lens, the correct distance measurement can be made with the standard lens, but when a photographic lens with a narrower angle of view is attached, the camera receives the echo reflected back from an object outside of the angle of view, so that the correct measurement of a distance to a subject cannot be attained and consequently an erratic measurement of distance results. On the other hand, if the directivity is determined depending upon the narrow angle of view of a telephoto lens, an erratic measurement of distance will result when a wide-angle lens is used.